wordlist

Virginia Tech strongly recommends using long (20+ char) passphrases for your VT accounts. Diceware is a method used to generate cryptographically strong passphrases. It is based on the principle that truly random selection of words from a wordlist can result in easily memorable passwords that are also extremely resistant to attack. Passwords that are six words or longer are thought to be safe for any very high security applications.

select the desired number of words



copyable text with spaces or dashes



entropy stats

There are words in your password, resulting in ~ bits of entropy (~12.92 bits/word, ~10 bits/letter, and ~5.16 bits/symbol). That many words equates to a total keyspace of ~ possible phrases (7776^WordsInPhrase). An adversary might get lucky and guess your phrase on the first try (extremely unlikely), or the brute-force attacker might be forced to try all of the keys in the keyspace to finally find that the last guess was the correct one. On average, it takes trying 50% of all phrases in the keyspace to find your phrase. The time it takes to discover your passphrase is based on how many guesses per second your attacker can muster. At the lower end in 2016 a small cluster of GPU's have demonstrated the ability to crack ~350 billion hashes/second. A nation state actor like the NSA may be able to perform quadrillions/second. Conservatively assuming a professional adversary can guess passwords at the rate of a keys/second, an exhaustive brute-force search on 50% of the total keyspace might take:

~ seconds

~ minutes

~ hours

~ days

~ years

~ avg. human lifespans

~ millenia

~ * age of the Universe

Learn more about calculating entropy

Frequently Asked Questions

How do I use it?

Click on one of the numbered passphrase generator buttons above. Click again to generate a totally new passphrase.

The + Word or + Symbol buttons will enhance the strength of the existing passphrase.

For extra security you can manually roll physical dice (two or five die rolls for each symbol or word respectively) and enter the results to add a word to your passphrase.

Each word or symbol displayed is shown with the index number that was used to look it up in the diceware word list.

You can copy the generated passphrase from the copyable string on the page. You should store it somewhere safe and secure. You might want to write it down and refer to the written version until you can remember it.

Close your browser window once you're done so others can't discover your passphrase.

Is it safe?

It depends. Are you the target of a nation-state level adversary? If so, you should probably not use this and should instead use Diceware to roll real physical dice and look up the words from the wordlist manually. This is the official recommendation of the Diceware FAQ. As a normal person, even if you have high security needs like protecting long term cryptographic keys, you should be safe using this tool. Using real dice is the most secure way, but relying on the random number generator should be safe as well.

Does this use a cryptographically strong random number generator to choose the words?

The JavaScript window.crypto.getRandomValues() CSPRNG that ships with modern browsers to get random bytes is used. You can learn more about window.crypto.getRandomValues() and make your own determination as to its suitability. Many cryptographic library authors are now targeting the browser environment and most are using this API as their primary source of entropy so you are in good company.

Does this application send any data anywhere?

No security sensitive information such as your selected passphrase size, die rolls, or the generated passphrase ever leaves your browser or is logged anywhere. Ever. Once the initial page is loaded as static files everything is done locally in your browser. In fact, once you load this application in your browser you can turn off your network connection and it should work just fine.

Where is the code for this application being served from?

The entire application is just HTML, JavaScript and CSS. There is no server side component and no database. All of the JavaScript and other assets are versioned in the repository and no code is served from outside of the repository.

How should I use this most safely?

You should ensure that:

  • You read about Diceware and understand the strengths and limitations of this approach.
  • Don't generate passphrases on a machine you don't own and control. No public machines!
  • Make sure no one else is in the room with you that can 'shoulder surf'.
  • You close the browser window, when you are done.
  • You always visit this site over a TLS (HTTPS) connection. This is enforced with HSTS. A non-TLS HTTP connection opens you up to trivial man-in-the-middle attack on the code or the wordlists.
  • You are using the latest version of a modern browser.

What is entropy?

Entropy is a measure of the uncertainty or randomness of a system. The concept is a difficult one to grasp fully and is confusing, even to experts. Strictly speaking, any given passphrase has an entropy of zero because it is already chosen. It is the method you use to randomly select your passphrase that has entropy. Entropy tells how hard it will be to guess the passphrase itself even if an attacker knows the method you used to select your passphrase. A passphrase is more secure if it is selected using a method that has more entropy.

Entropy is measured in bits. The outcome of a single coin toss -- "heads or tails" -- has one bit of entropy.

Arnold G. Reinhold - Diceware FAQ

How are you measuring entropy?

Each standard Diceware word is assigned ~12.92 bits of entropy (Math.log2(7776)), each special character added is ~5.16 bits (Math.log2(36)). The total is the sum of the entropy in each full word or special character.

Who created this?